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Robert Poulin - One of the best experts on this subject based on the ideXlab platform.
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interactions between parasites of the Cockle austrovenus stutchburyi hitch hikers resident cleaners and habitat facilitators
Parasitology, 2007Co-Authors: Tommy L F Leung, Robert PoulinAbstract:The patterns of association between parasites within a particular host are determined by a number of factors. One of these factors is whether or not infection by one parasite influences the probability of acquiring other parasite species. This study investigates the pattern of association between various parasites of the New Zealand Cockle Austrovenus stutchburyi. Hundreds of Cockles were collected from one locality within Otago Harbour, New Zealand and examined for trematode metacercariae and other symbionts. Two interspecific associations emerged from the study. First, the presence of the myicolid copepod Pseudomyicola spinosus was positively associated with higher infection intensity by echinostomes. The side-effect of the copepod's activities within the Cockle is suggested as the proximate mechanism that facilitates infection by echinostome cercariae, leading to a greater rate of accumulation of metacercariae in Cockles harbouring the copepod. Second, a positive association was also found between infection intensity of the metacercariae of foot-encysting echinostomes and that of gymnophallid metacercariae. This supports earlier findings and suggests that the gymnophallid is a hitch-hiker parasite because, in addition to the pattern of positive association, it (a) shares the same transmission route as the echinostomes, and (b) unlike the echinostomes, it is not capable of increasing the host's susceptibility to avian predation. Thus, both active hitch-hiking and incidental facilitation lead to non-random infection patterns in this parasite community.
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parasites boost biodiversity and change animal community structure by trait mediated indirect effects
Oikos, 2005Co-Authors: Kim N Mouritsen, Robert PoulinAbstract:Parasitism has long been emphasised as an important process structuring animal communities. However, empirical evidence documenting the impact of parasites in other than simple laboratory settings is lacking. Here we examine the trait-mediated indirect effects of echinostome trematodes on a New Zealand soft bottom intertidal community of macroinvertebrates. Curtuteria australis and a second related but undescribed trematode both utilise the Cockle Austrovenus stutchburyi as second intermediate host in which the parasites infect the foot tissue. Heavily infected Cockles are therefore more sessile than lightly infected individuals, and, unable to bury, often rest on the sediment surface. We utilised these behavioural changes in two long term field experiments, respectively manipulating the parasite load of buried Cockle (i.e. bioturbation), and the density of surfaced Cockles (i.e. surface structures and seabed hydrodynamics). Both high parasite loads in buried Cockles and the presence of surfaced Cockles increased species richness and generally also the density of certain species and of major systematic and functional groups of benthic macroinvertebrates. Species diversity (alpha) peaked under intermediate densities of surfaced Cockles. Our results demonstrate that parasites, solely through their impact on the behaviour of a single community member, can be significant determinants of animal community structure and function.
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equal partnership two trematode species not one manipulate the burrowing behaviour of the new zealand Cockle austrovenus stutchburyi
Journal of Helminthology, 2004Co-Authors: C Babirat, Kim N Mouritsen, Robert PoulinAbstract:Metacercariae of the trematode Curtuteria australis (Echinostomatidae) accumulate in the foot of the New Zealand Cockle Austrovenus stutchburyi, severely impairing the Cockle’s ability to burrow under the sediments. This results in increased predation by birds on Cockles, and thus enhanced transmission rates of the parasite to its bird definitive hosts. This host manipulation by the trematode is costly: fish regularly crop the tip of the foot of Cockles stranded on the sediment surface, killing any metacercariae they ingest. A second, previously undetected trematode species (characterized by 23 collar spines) co-existing with C. australis, has been found in the foot of Cockles in the Otago Harbour, South Island, New Zealand. The relative abundance of the two species varies among localities, with the identity of the numerically dominant species also changing from one locality to the next. Both C. australis and the new species have a strong preference for encysting in the tip of the Cockle’s foot, where their impact on the burrowing ability of the host is greatest, and where they both face the risk of cropping by fish. Results indicate that these two species are ecological equivalents, and their combined numbers determine how the Cockle population is affected.
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parasite induced surfacing in the Cockle austrovenus stuchburyi adaptation or not
Journal of Evolutionary Biology, 2004Co-Authors: D M Tompkins, Kim N Mouritsen, Robert PoulinAbstract:Parasite manipulation of host behaviour is a compelling example of the extended phenotype. However, in many cases, such manipulation may be incorrectly assumed. Previous work has demonstrated that Austrovenus stuchburyi Cockles stranded on mud-flat surfaces due to an inability to re-burrow both contain significantly more metacercariae of the trematode Curtuteria australis and are predated by the definitive host of this parasite at a faster rate than burrowed Cockles. These results have been interpreted as strong evidence for a manipulation of Cockle behaviour by the trematode to facilitate transmission to the definitive host. The model presented here, however, indicates that the selective advantage to the parasite of the altered host behaviour is currently of a negligible level at our study site that is highly unlikely to have been realized as an adaptation over evolutionary time. Hence, there are no grounds on which the more parsimonious explanation, that the altered host behaviour observed is simply an incidental side-effect of infection, can be rejected. We thus maintain that for any change in the behaviour of infected hosts to be confirmed as potentially a parasite trait that has evolved in response to selection, the adaptive benefit taking into account the entire parasite life cycle may need to be considered.
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Spatial heterogeneity in parasite loads in the New Zealand Cockle: the importance of host condition and density
Journal of the Marine Biological Association of the United Kingdom, 2003Co-Authors: Kim N Mouritsen, S. Mckechnie, E. Meenken, J.l. Toynbee, Robert PoulinAbstract:Samples of the New Zealand Cockle Austrovenus stutchburyi (Veneridae) collected at two diierent intertidal levels were found to be heavily infected by the echinostome trematode Curtuteria australis which use the mud £at whelk Cominella glandiformis and shorebirds as ¢rst and de¢nitive host, respectively. Parasite loads were on average more than 2-fold higher at the high site than at the low site, whereas the density of Curtuteria australis metacercariae per square metre showed the opposite trend. This pattern appeared unrelated to the abundance of ¢rst intermediate hosts and C. australis prevalence within this host that did not diier between sites. At both sites there was a positive relationship between parasite load and Cockle condition, a likely byproduct of the relationship between condition-based ¢ltration capacity and the rate at which individual Cockles encounter the free-swimming trematode larvae. The results suggest that the between-site variation in parasitism is a consequence of the much higher density of Cockles at the low site. There, the dense Cockle population is able to clear the water column of parasites and consequently individual Cockles virtually ‘compete’ for parasite larvae. This will depress mean infection intensity per Cockle but elevate mean parasite density per square metre.
Kim N Mouritsen - One of the best experts on this subject based on the ideXlab platform.
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parasites boost biodiversity and change animal community structure by trait mediated indirect effects
Oikos, 2005Co-Authors: Kim N Mouritsen, Robert PoulinAbstract:Parasitism has long been emphasised as an important process structuring animal communities. However, empirical evidence documenting the impact of parasites in other than simple laboratory settings is lacking. Here we examine the trait-mediated indirect effects of echinostome trematodes on a New Zealand soft bottom intertidal community of macroinvertebrates. Curtuteria australis and a second related but undescribed trematode both utilise the Cockle Austrovenus stutchburyi as second intermediate host in which the parasites infect the foot tissue. Heavily infected Cockles are therefore more sessile than lightly infected individuals, and, unable to bury, often rest on the sediment surface. We utilised these behavioural changes in two long term field experiments, respectively manipulating the parasite load of buried Cockle (i.e. bioturbation), and the density of surfaced Cockles (i.e. surface structures and seabed hydrodynamics). Both high parasite loads in buried Cockles and the presence of surfaced Cockles increased species richness and generally also the density of certain species and of major systematic and functional groups of benthic macroinvertebrates. Species diversity (alpha) peaked under intermediate densities of surfaced Cockles. Our results demonstrate that parasites, solely through their impact on the behaviour of a single community member, can be significant determinants of animal community structure and function.
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equal partnership two trematode species not one manipulate the burrowing behaviour of the new zealand Cockle austrovenus stutchburyi
Journal of Helminthology, 2004Co-Authors: C Babirat, Kim N Mouritsen, Robert PoulinAbstract:Metacercariae of the trematode Curtuteria australis (Echinostomatidae) accumulate in the foot of the New Zealand Cockle Austrovenus stutchburyi, severely impairing the Cockle’s ability to burrow under the sediments. This results in increased predation by birds on Cockles, and thus enhanced transmission rates of the parasite to its bird definitive hosts. This host manipulation by the trematode is costly: fish regularly crop the tip of the foot of Cockles stranded on the sediment surface, killing any metacercariae they ingest. A second, previously undetected trematode species (characterized by 23 collar spines) co-existing with C. australis, has been found in the foot of Cockles in the Otago Harbour, South Island, New Zealand. The relative abundance of the two species varies among localities, with the identity of the numerically dominant species also changing from one locality to the next. Both C. australis and the new species have a strong preference for encysting in the tip of the Cockle’s foot, where their impact on the burrowing ability of the host is greatest, and where they both face the risk of cropping by fish. Results indicate that these two species are ecological equivalents, and their combined numbers determine how the Cockle population is affected.
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parasite induced surfacing in the Cockle austrovenus stuchburyi adaptation or not
Journal of Evolutionary Biology, 2004Co-Authors: D M Tompkins, Kim N Mouritsen, Robert PoulinAbstract:Parasite manipulation of host behaviour is a compelling example of the extended phenotype. However, in many cases, such manipulation may be incorrectly assumed. Previous work has demonstrated that Austrovenus stuchburyi Cockles stranded on mud-flat surfaces due to an inability to re-burrow both contain significantly more metacercariae of the trematode Curtuteria australis and are predated by the definitive host of this parasite at a faster rate than burrowed Cockles. These results have been interpreted as strong evidence for a manipulation of Cockle behaviour by the trematode to facilitate transmission to the definitive host. The model presented here, however, indicates that the selective advantage to the parasite of the altered host behaviour is currently of a negligible level at our study site that is highly unlikely to have been realized as an adaptation over evolutionary time. Hence, there are no grounds on which the more parsimonious explanation, that the altered host behaviour observed is simply an incidental side-effect of infection, can be rejected. We thus maintain that for any change in the behaviour of infected hosts to be confirmed as potentially a parasite trait that has evolved in response to selection, the adaptive benefit taking into account the entire parasite life cycle may need to be considered.
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Intertidal facilitation and indirect effects: causes and consequences of crawling in the New Zealand Cockle
Marine Ecology Progress Series, 2004Co-Authors: Kim N MouritsenAbstract:Bioturbation by the ghost shrimp Callianassa filholi and the lugworms Abarenicola affi- nis as well as coverage by macroalgae cause the New Zealand Cockle Austrovenus stutchburyi (Veneridae) to relocate by crawling longer distances on the sediment surface. On the surface, the Cockles become targets for sublethal predation by benthic-feeding fishes, which crop off their feet. This renders the Cockles unable to bury for up to 8 wk, thus exposing them to a 5-fold higher preda- tion pressure from shorebirds and the whelk Cominella glandiformis than buried conspecifics. Shell dimensions, foot size, general condition, gender, age, and infections by gymnophallid trematodes do not influence the crawling activity of Cockles. However, heavy infection by the digenean trematode Curtuteria australis and the shell-boring spionid polychaete Boccardia acus reduces the distance travelled, and these organisms may hence reinforce the impact of the biogenic disturbers by forcing repeated crawling of the Cockles to reach an undisturbed site. The presence of biogenic disturbers and some parasites therefore benefits predating fishes by providing them with an otherwise inacces- sible food source, and these in turn benefit birds and whelks through foot-cropping, thus increasing the availability of prey. The gymnophallids also receive an advantage through transmission success to their definitive shorebird hosts. The question as to whether Curtuteria australis benefits, depends on the balance between its loss to fishes (unsuitable hosts) and its increased trophic transmission to its bird hosts. The spionid B. acus on the other hand is negatively affected, since its fate is linked to that of its substrate, which is the shell of the Cockle. If the Cockle is predated, the attached B. acus will perish also.
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Spatial heterogeneity in parasite loads in the New Zealand Cockle: the importance of host condition and density
Journal of the Marine Biological Association of the United Kingdom, 2003Co-Authors: Kim N Mouritsen, S. Mckechnie, E. Meenken, J.l. Toynbee, Robert PoulinAbstract:Samples of the New Zealand Cockle Austrovenus stutchburyi (Veneridae) collected at two diierent intertidal levels were found to be heavily infected by the echinostome trematode Curtuteria australis which use the mud £at whelk Cominella glandiformis and shorebirds as ¢rst and de¢nitive host, respectively. Parasite loads were on average more than 2-fold higher at the high site than at the low site, whereas the density of Curtuteria australis metacercariae per square metre showed the opposite trend. This pattern appeared unrelated to the abundance of ¢rst intermediate hosts and C. australis prevalence within this host that did not diier between sites. At both sites there was a positive relationship between parasite load and Cockle condition, a likely byproduct of the relationship between condition-based ¢ltration capacity and the rate at which individual Cockles encounter the free-swimming trematode larvae. The results suggest that the between-site variation in parasitism is a consequence of the much higher density of Cockles at the low site. There, the dense Cockle population is able to clear the water column of parasites and consequently individual Cockles virtually ‘compete’ for parasite larvae. This will depress mean infection intensity per Cockle but elevate mean parasite density per square metre.
Xavier De Montaudouin - One of the best experts on this subject based on the ideXlab platform.
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Parasite Assemblages in a Bivalve Host Associated with Changes in Hydrodynamics
Estuaries and Coasts, 2020Co-Authors: Simão Correia, Xavier De Montaudouin, Ana Picado, Rosa Freitas, Rui J. M. Rocha, João M. Dias, Luísa MagalhãesAbstract:Studies on marine community structure and their modulation by horizontal and vertical abiotic gradients have focused on free-living species, neglecting parasites despite their important role in ecosystems. Field observations, a laboratory flume experiment and modelling were used to examine parasite infection patterns related to host tidal and spatial position along a Portuguese coastal lagoon (Ria de Aveiro). Cockles ( Cerastoderma edule ) and trematodes were used as a host-parasite model to test the hypotheses: (1) higher infection levels in subtidal Cockles, positioned downstream and (2) higher current velocity in downstream areas with consequent higher Cockle infection. Cockles were collected from two spatial and tidal positions in two seasons. The relationship between current velocity and Cockle infection was examined experimentally by exposing Cockles to cercariae of Himasthla elongata at two current velocities. Intertidal Cockles displayed higher infection, highlighting vertical position as an important driver of infection possibly due to first host proximity and/or trematode life cycle facilitation (higher Cockle exposure to final host predation). The hydrodynamic model showed that the Ria de Aveiro was abiotically heterogenous with Cockles displaying higher infection levels in the downstream area. Multiple regression analysis demonstrated a positive correlation between salinity, dissolved oxygen, current velocity and trematode abundance. The influence of current velocity on infection success was corroborated experimentally. The present study demonstrated the importance of host vertical and horizontal position on trematode infection, highlighting the positive influence of current velocity by supporting settlement and promoting favourable abiotic conditions.
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Ecosystem services provided by a non-cultured shellfish species: The common Cockle Cerastoderma edule
Marine Environmental Research, 2020Co-Authors: Aurélie Ciutat, Xavier De Montaudouin, Rosa Fernández Otero, Mónica Incera Filgueira, David Carss, Ana Brito, Paula Chainho, Angus Garbutt, M. Anouk Goedknegt, Sharon LynchAbstract:Coastal habitats provide many important ecosystem services. The substantial role of shellfish in delivering ecosystem services is increasingly recognised, usually with a focus on cultured species, but wild-harvested bivalve species have largely been ignored. This study aimed to collate evidence and data to demonstrate the substantial role played by Europe's main wild-harvested bivalve species, the common Cockle Cerastoderma edule, and to assess the ecosystem services that Cockles provide. Data and information are synthesised from five countries along the Atlantic European coast with a long history of Cockle fisheries. The Cockle helps to modify habitat and support biodiversity, and plays a key role in the supporting services on which many of the other services depend. As well as providing food for people, Cockles remove nitrogen, phosphorus and carbon from the marine environment, and have a strong cultural influence in these countries along the Atlantic coast. Preliminary economic valuation of some of these services in a European context is provided, and key knowledge gaps identified. It is concluded that the Cockle has the potential to become (i) an important focus of conservation and improved sustainable management practices in coastal areas and communities, and (ii) a suitable model species to study the integration of cultural ecosystem services within the broader application of 'ecosystem services'.
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Interactive effects of contamination and trematode infection in Cockles biochemical performance
Environmental Pollution, 2018Co-Authors: Luísa Magalhães, Xavier De Montaudouin, Etelvina Figueira, Rosa FreitasAbstract:Abstract Anthropogenic activities, especially those involving substances that pollute the environment can interfere with bivalve populations, as well as parasitism, a fundamental ecological interaction often neglected. In marine environments, organisms are concomitantly exposed to pollutants and parasites, a combination with synergistic, antagonistic or additive effects representing a potential threat to aquatic communities sustainability. In the present study, Cerastoderma edule (the edible Cockle)–Himasthla elongata (trematode) was used as host–parasite model. Cockles are worldwide recognized as good sentinel and bioindicator species and can be infected by several trematodes, the most abundant macroparasites in coastal waters. Tested hypotheses were: 1) Cockles exposed to increasing parasite pressure will present greater stress response; 2) Cockles exposure to arsenic (single concentration test: 5.2 μg L−1) will change parasite infection success and Cockles stress response to infection. Arsenic was used for being one of the most common pollutants in the world and stress response assessed using biochemical markers of glycogen content, metabolism, antioxidant activity and cellular damage. Results showed that intensity of parasite pressure was positively correlated to biochemical response, mainly represented by higher metabolic requirements. Contamination did not affect parasite infection success. Compared to arsenic, trematode infection alone exerted a stronger impact: higher glycogen storage, metabolism and cellular damage and antioxidant activity inhibition. In interaction, parasitism and arsenic reduced hosts metabolism and cellular damage. Therefore, to a certain extent and in a contamination scenario, Cockles may benefit from trematode infection, working as a protection for the pollutant accumulation in the organisms, reducing overall ROS production, which can consequently led to less toxic effects. These findings highlighted the deleterious effects of trematode infection in their hosts and showed the importance of including parasitology in ecotoxicological studies.
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Cockle infection by himasthla quissetensis i from cercariae emergence to metacercariae infection
Journal of Sea Research, 2016Co-Authors: Xavier De Montaudouin, Hugues Blanchet, Celine Desclauxmarchand, Nicolas Lavesque, Guy BacheletAbstract:Abstract The European Cockle ( Cerastoderma edule ) is an exploited bivalve along the North-Eastern Atlantic semi-sheltered ecosystems. Its population dynamics are driven by numerous environmental factors, including parasitism, particularly by trematodes. The complex life cycle of trematodes includes a free living stage (cercaria) between the first (a mollusk) and the second (an invertebrate or a vertebrate) intermediate hosts. Taking the example of Himasthla quissetensis , a dominant trematode in Arcachon Bay (France) utilizing Nassarius reticulatus as first intermediate host and the Cockle as second intermediate host, we investigated the correlation between Cockle infection and cercariae emergence by N. reticulatus , including the role of water temperature and light. Experimental and field data provided evidence that cercariae emergence from N. reticulatus took place during the night and for water temperature comprised between 15 °C and 22 °C (optimum at 20 °C). The lifespan of cercariae did not exceed 48 h and 50% of them were no more infectious after 7 h. A model was designed (emergence = f(water temperature)) in order to calculate an average monthly cercarial emergence rate according to water temperature that was daily recorded for 5 years (1998–2002). Concomitantly, non-infected Cockles were transplanted each of these years in order to assess the infection rate by H. quissetensis . Infection occurred strictly for the same water temperatures (and dates) as those expected for cercariae emergence. Within each year, there was often (but not always) a good correlation between the predicted number of emerging cercariae and the observed number of cercariae transformed into metacercariae in Cockles. However, the among-years variability of Cockle infection (× 4.4 range) was not explained by the predicted annual number of emerging cercariae. This study highlights the importance of water temperature and light in stimulating cercariae emergence which is closely related to the occurrence of Cockle infection. Accordingly, climate change would be expected to alter certain parasite transmission traits. Conversely, the lack of correlation between the total number of metacercariae in Cockles and the expected number of cercariae suggests that other factors contribute to infestation variability.
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Assessing parasite community structure in Cockles Cerastoderma edule at various spatio-temporal scales
Estuarine Coastal and Shelf Science, 2012Co-Authors: Xavier De Montaudouin, Cindy Binias, Géraldine LassalleAbstract:Abstract Cockles ( Cerastoderma edule ) are among the most exploited bivalves in Europe. They live in lagoons and estuaries where they undergo many stressors including parasites. Trematodes are the most prevalent macroparasites of Cockles and can exert a significant impact on their host populations depending on parasite species and infection intensity. Monitoring these parasite–host systems in order to predict potential host mortalities require a correct knowledge of the spatio-temporal variation of infection. A yearly monitoring of Cockles from six stations around Ile aux Oiseaux, Arcachon Bay (France) was conducted between 1998 and 2005. Distance between two stations was ca. 1 km. Nine trematode species were identified. Despite a relative homogeneity of the parasite community structure in Cockles, between three and six clusters were identified by Hierarchical Ascendant Classification showing that among-sites heterogeneity of trematode communities in Cockles was higher than within-site heterogeneity. At the scale of 8 years, and for 2-year old Cockles, these patterns remained stable in four out of six stations. Spatial aggregation disappeared with Cockle age, since parasite communities in 3-year Cockles did not reflect any particular station(s): with age, Cockles eventually accumulated most trematode species and lost the site signature. On the other hand, we demonstrated that the commonly accepted theory stating that older/larger Cockles accumulate more trematode larvae was not verified and that there could exist a vulnerable age/size that doesn’t correspond to largest values. This study provided a new insight in the parasite community heterogeneity in their host, and in the significance of samples in relation with space and time.
R. Dekker - One of the best experts on this subject based on the ideXlab platform.
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winters not too cold summers not too warm long term effects of climate change on the dynamics of a dominant species in the wadden sea the Cockle cerastoderma edule l
Marine Biology, 2020Co-Authors: J.j. Beukema, R. DekkerAbstract:The Wadden Sea experiences a warming climate with water temperatures having increased by about 2 °C during the last 50 years. We studied possible effects of this temperature rise on the dynamics of a Cockle (Cerastoderma edule) population in the westernmost part of the Wadden Sea by monitoring the numbers of aged Cockles since the early 1970s. We found increased rates of mortality at extreme climatic conditions. In particular, survival declined to close-to-0 in all age classes in severe winters. In the hottest summers, survival was somewhat reduced in older (> 1 year old) Cockles. On the other hand, recruitment was enhanced after cold winters, but this was not a direct effect of low temperatures as it was mainly caused by a reduction of the abundance of predators on small spat. The observed decline of the long-term trend in recruitment was compensated by an increasing trend of winter survival, resulting in an absence of any long-term trend in adult numbers.
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The intertidal zoning of Cockles (Cerastoderma edule) in the Wadden Sea, or why Cockle fishery disturbed areas of relatively high biodiversity
Helgoland Marine Research, 2009Co-Authors: Jan Jacobus Beukema, R. DekkerAbstract:Recently, Kraan et al. (ICES J Mar Sci 64:1735–1742, 2007 ) reported that areas in the Wadden Sea selected by mechanical Cockle dredgers were of greater zoobenthic diversity than areas that remained undredged. The present paper attempts to explain this observation, focussing on the elevation-related zoning of the macrobenthic fauna on tidal flats. Dense beds of Cockles Cerastoderma edule occur in a specific intermediate intertidal-height zone where more species are present (and reach their maximal abundance) than in either lower or higher zones. This coincidence of preferred intertidal zones in many species, including Cockles, may cause the higher species richness (and higher total macrozoobenthic biomass) of the fisher-chosen dredging areas as compared to other nearby non-dredged tidal-flat areas.
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The intertidal zoning of Cockles () in the Wadden Sea, or why Cockle fishery disturbed areas of relatively high biodiversity
Helgoland Marine Research, 2009Co-Authors: Jan Jacobus Beukema, R. DekkerAbstract:Recently, Kraan et al. (ICES J Mar Sci 64:1735–1742, 2007) reported that areas in the Wadden Sea selected by mechanical Cockle dredgers were of greater zoobenthic diversity than areas that remained undredged. The present paper attempts to explain this observation, focussing on the elevation-related zoning of the macrobenthic fauna on tidal flats. Dense beds of Cockles occur in a specific intermediate intertidal-height zone where more species are present (and reach their maximal abundance) than in either lower or higher zones. This coincidence of preferred intertidal zones in many species, including Cockles, may cause the higher species richness (and higher total macrozoobenthic biomass) of the fisher-chosen dredging areas as compared to other nearby non-dredged tidal-flat areas.
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annual Cockle cerastoderma edule production in the wadden sea usually fails to sustain both wintering birds and a commercial fishery
Marine Ecology Progress Series, 2006Co-Authors: J.j. Beukema, R. DekkerAbstract:Low Cockle Cerastoderma edule stocks in the Dutch Wadden Sea over the last ~15 yr have caused ecological problems, including declines in numbers of some specialized bird species and a sharpening conflict between nature conservationists and fishermen. To study why Cockle produc- tion and resulting biomass of adult Cockles failed, we analyzed long-term (1973 to 2003) data on annual and cohort production of Cockles in the Balgzand tidal flat area in the westernmost part of the Wadden Sea. Somatic production was estimated from summed growth increments per half-year period and expressed in ash-free dry weight (AFDW). In adults, positive values in April to August regularly alternated with negative values in September to March, when up to 60% of individual weight gains in the preceding season were lost. Life-time production averaged 0.06 g AFDW for ~3 mo old recruits and 0.21 g for ~10 mo old recruits. The numerical recruit density of a cohort as observed after their first winter predicted subsequent life-time cohort production within narrow lim- its. The 31 yr mean of net somatic production amounted to 7.3 g AFDW m -2 yr -1 . The period of largest production during the lifetime of a cohort occurred during their second growing season (when cock- les grow from spat to adult size). Years with high production values occurred 1 yr after a highly suc- cessful reproductive season, and high biomasses were achieved 1 to 3 yr after a highly successful sea- son. In contrast, low values were observed when a successful recruitment had been >3 yr in the past, and also after severe winters (causing high Cockle mortality). Local variation in mean annual produc- tion was primarily related to local variation in recruitment success; however, production per recruit was significantly higher at low than at high intertidal levels. The main cause of low biomass values observed in recent years was failing recruitment in off-shore areas. As a consequence, in nearly all of the last 15 years, Cockles have been too scarce in the western Wadden Sea to sustain both wintering birds and a commercial fishery.
Phillip S Rainbow - One of the best experts on this subject based on the ideXlab platform.
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effects of environmental and physiological variables on the accumulated concentrations of trace metals in the new zealand Cockle austrovenus stutchburyi
Science of The Total Environment, 2014Co-Authors: Islay D. Marsden, B D Smith, Phillip S RainbowAbstract:Abstract We examined potential causes of variation in trace element accumulation in an estuarine bivalve Austrovenus stutchburyi from two estuarine systems in South Island, New Zealand which differed in their metal contamination and salinity regimes. Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn were measured (ICP-OES) in whole body tissues of bivalves collected from 10 sites, seston collected at high tide (a potential food resource) and in the sediment at the sites. All 13 elements showed a relationship between log bioaccumulated trace element concentration (mg kg − 1 dry weight tissue) and log shell length (mm), either in the whole data set or at least one site (ANCOVA). Growth rates of Cockles varied significantly amongst sites. Accumulated soft tissue concentrations of Ag, As, Co and Cr increased with age of Cockle, those of Pb and Zn decreased, with no clear age-related trend for the remaining metals (ANCOVA). Shell length was generally a good proxy for age when allowing for any size effect in metal accumulation by the Cockle. There was no consistent pattern between the estuarine systems, probably reflecting unidentified contaminant inputs. Following depuration, tissue concentrations decreased significantly for some elements (Fe, Mn, Ti and V), indicating high concentrations of these metals in the gut contents. Trace element concentrations in the seston generally did not correlate with the bivalve tissue concentrations. There were few (Spearman's Rank) correlations between environmental variables at the time of sampling and Cockle tissue trace element concentrations. The main sources of variation in bioaccumulated trace metal concentrations in the whole tissues of the Cockle are location, shell length and age.